definitive

An important or final judgment about someone or something is definitive.

You might hear a movie review say that "this film is definitive proof of the actor's talent." Here they mean it's the ultimate example that shows how skilled this person is. When you think about it, the word "definitive" can help you understand that this film is not just good or impressive - it's the best and most convincing one. This is why critics often use "definitive" when talking about a movie that sets the standard for others in its genre.

If someone uses "definitive" to describe a book, they might be saying that this particular work is the ultimate authority on the subject, and any other books should be compared to it.